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Revista Brasileira de Entomologia 60 (2016) 231–237

REVISTA BRASILEIRA DE

EntomologiaA Journal on Insect Diversity and Evolution

www.rbentomologia .com

ystematics, Morphology and Biogeography

irst larval description and chaetotaxic analysis of the neotropicalhirligig beetle genus Enhydrus Laporte (Coleoptera, Gyrinidae)

ariano C. Michata,∗, Thiago Marinho Alvarengab, Marconi Souza Silvac, Yves Alaried

Universidad de Buenos Aires, Instituto de Biodiversidad y Biología Experimental y Aplicada, Departamento de Biodiversidad y Biología Experimental, Laboratorio de Entomología,uenos Aires, ArgentinaUniversidade Estadual de Campinas, Instituto de Biologia, Programa de Doutorado em Biologia Animal, Campinas, SP, BrazilUniversidade Federal de Lavras, Centro de Estudos em Biologia Subterrânea, Departamento de Biologia, Lavras, MG, BrazilLaurentian University, Department of Biology, Sudbury, Canada

r t i c l e i n f o

rticle history:eceived 24 March 2016ccepted 30 May 2016vailable online 16 June 2016ssociate Editor: Lúcia M. Almeida

eywords:dephagaineutiniorphometry

a b s t r a c t

The larva of the whirligig beetle Enhydrus sulcatus (Wiedemann, 1821) is described and illustrated forthe first time, including detailed morphometric and chaetotaxic analyses of the cephalic capsule, headappendages and legs. Larvae of Enhydrus Laporte, 1834 exhibit the characters traditionally recognized asautapomorphies of the family Gyrinidae: well developed cardo, completely divided prementum, presenceof lateral abdominal tracheal gills, and presence of four terminal hooks on the pygopod. The egg bursterslocated on the parietal, the presence of an additional sensorial plate on the third antennomere, and awell developed lacinia may also represent autapomorphies of the family. Enhydrus larvae share withthose of the other known Dineutini genera the presence of numerous minute additional setae on themandible, the presence of additional setae on the cardo, the submedial position of the coxal seta CO12,

eotropicsensilla

the absence of the trochanteral seta TR2, and the presence of numerous pore-like additional structures onthe ultimate maxillary and labial palpomeres. On the other hand, Enhydrus can be distinguished from theother known dineutine genera by the presence of pore-like additional structures on the basal maxillaryand labial palpomeres, the presence of ventral spinulae on the pygopod, and the bare tracheal gills, amongother characters.

e Brahe CC

© 2016 Sociedadaccess article under t

ntroduction

Enhydrus Laporte, 1834 is a small gyrinid genus composed ofour species (Miller and Bergsten, 2012). It is included in the tribeineutini together with the extant genera Andogyrus Ochs, 1924,ineutus MacLeay, 1825, Macrogyrus Régimbart, 1882 and Por-

orhynchus Laporte, 1835, and several extinct genera (Gustafsonnd Miller, 2013). Members of this genus are relatively large (adultength about 20 mm) and occur mainly in South America, with twopecies (E. sulcatus (Wiedemann, 1821) and E. tibialis Régimbart,877) in Brazil, one species (E. mirandus Ochs, 1955) in Venezuela,nd the remaining species (E. atratus Régimbart, 1877) in Ecuadornd Colombia but reaching Panamá and Costa Rica in Central Amer-ca. The known southern limit of the genus is a record of E. sulcatus

n the state of Rio Grande do Sul, southern Brazil (Manko, 1993).he adult members of Enhydrus were revised by Brinck (1978).

∗ Corresponding author.E-mail: marianoide@gmail.com (M.C. Michat).

http://dx.doi.org/10.1016/j.rbe.2016.05.005085-5626/© 2016 Sociedade Brasileira de Entomologia. Published by Elsevier Editorreativecommons.org/licenses/by-nc-nd/4.0/).

sileira de Entomologia. Published by Elsevier Editora Ltda. This is an open BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Enhydrus sulcatus, the type species, inhabits streams that runthrough hills of preserved gallery forest, and within this habitatthe adults can be found, either isolated or in aggregations, in thestreams or in small pools formed by the intricate geography ofthe stream borders, always in shaded places with some current(Manko, 1997; Alvarenga et al., 2011). This species has been subjectof detailed studies on the adult external and internal morphology(Manko, 1993), morphometry and sexual dimorphism (Alvarengaet al., 2011), pygidial glands (Barth, 1960), and bionomy and habi-tat (Manko, 1997). However, the study of the larvae has remained agap in our knowledge, with this stage being unknown for the genus.

A system of nomenclature for the primary sensilla of lar-vae of the family Gyrinidae is presently under development(Archangelsky and Michat, 2007; Michat et al., 2010; Michat andGustafson, 2016). Although incomplete and subject to improve-ment based on the discovery of more gyrinid larvae, this systemprovides a descriptive template to which larvae of more genera

can be incorporated. In this contribution we study the first-instarlarva of E. sulcatus to provide, for the first time, a detailed descrip-tion of the larval morphology and primary chaetotaxy of the genusEnhydrus. We also compare the morphological and chaetotaxic

a Ltda. This is an open access article under the CC BY-NC-ND license (http://

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haracters of this genus with those of other gyrinid genera for whichhe larvae have been described in detail, and discuss remarkable ornteresting findings.

aterial and methods

ource of material

The description provided in this paper is based on five instar specimens obtained from eggs laid by adults collected in June009 at the following locality: Brazil, Minas Gerais State, Ingaí,1◦20′47′′S & 44◦59′27′′W. Females were kept alive in plastic wateranks and fed with small insects. The oviposition occurred two daysfter confinement, and the eggs hatched 28 days after oviposition.he larvae could not be successfully reared in the laboratory due toheir unknown requirements.

ethods

The larvae were cleared in lactic acid, dissected, and mountedn glass slides in polyvinyl-lacto-glycerol. Microscopic examina-ion at magnifications up to 1000× and drawings were made usingn Olympus CX31 compound microscope equipped with a cameraucida. Drawings were scanned and digitally inked using a GeniusenSketch tablet. The material is held in the collections of Y. AlarieDepartment of Biology, Laurentian University, Sudbury, Ontario,anada) and M.C. Michat (Laboratory of Entomology, Buenos Airesniversity, Argentina).

orphometric analysis

We employed the terms used in previous papers dealing withhe larval morphology of Gyrinidae (Archangelsky and Michat,007; Michat et al., 2010). The following measurements were takenwith abbreviations shown in parentheses). Total length (excludingerminal tracheal gills) (TL); maximum width (excluding trachealills) (MW); head length (HL) (total head length including therontoclypeus, measured medially along the epicranial stem); max-mum head width (HW); length of frontoclypeus (from anterior

argin to the joint of frontal and coronal sutures) (FRL); occipitaloramen width (maximum width measured along dorsal marginf occipital foramen) (OCW); coronal suture length (COL); lengthf mandible (MNL) (measured from laterobasal angle to apex);idth of mandible (MNW) (maximum width measured at base);

ength of maxillary palpifer (PPF); length of galea (GA). Length ofntenna (A), maxillary (MP) and labial (LP) palpi were derived bydding the lengths of the individual segments; each segment isenoted by the corresponding letter(s) followed by a number (e.g.,1, first antennomere). The maxillary palpus was considered aseing composed of three segments united to the stipes through

palpifer (Archangelsky and Michat, 2007). Length of leg, includ-ng the longest claw (CL), was derived by adding the lengths of thendividual segments; each leg is denoted by the letter L followedy a number (e.g., L1, prothoracic leg); the length of trochanter

ncludes only the proximal portion, considered from the base tohe beginning of the femur; the leg was considered as being com-osed of six segments (Lawrence, 1991). Length of terminal hooksf abdominal segment X, separated in medial hook (MH) and lat-ral hook (LH). These measurements were used to calculate severalatios that characterize body shape.

haetotaxic analysis

Primary setae and pores were distinguished on the cephalic cap-ule, head appendages and legs. Sensilla were coded by two capitaletters, in most cases corresponding to the first two letters of the

Entomologia 60 (2016) 231–237

name of the structure on which they are located, and a number(setae) or a lower case letter (pores). The following abbreviationswere used: AN, antenna; CO, coxa; FE, femur; FR, frontoclypeus;LA, labium; MN, mandible; MX, maxilla; PA, parietal; PT, pretar-sus; TA, tarsus; TI, tibia; TR, trochanter. Setae and pores present inthe first-instar larva of E. sulcatus were labeled by comparison withprevious papers dealing with the primary chaetotaxy of membersof the family Gyrinidae (Archangelsky and Michat, 2007; Michatet al., 2010). Homologies were recognized using the criterion ofsimilarity of position (Wiley, 1981). Setae located at the apices ofthe maxillary and labial palpi were extremely difficult to distin-guish due to their position and small size. Accordingly, they are notwell represented in the drawings.

Results

Description of the first-instar larva of Enhydrus sulcatus(Wiedemann, 1821)

DiagnosisLarvae of Enhydrus can be distinguished from those of other

known gyrinid genera by the following combination of char-acters: cephalic capsule constricted at level of occipital region(Figs. 2, 4 and 5); occipital suture present (Figs. 2 and 4); coro-nal suture short; medial lobe of FR with four very inconspicuousteeth (Figs. 2 and 4); lacinia not dentate on posterior margin,indented apically (Figs. 9 and 10); claws lacking basoventral spinu-lae (Figs. 13 and 14); tracheal gills lacking spinulae (Fig. 3); terminalhooks subequal in length (Figs. 3 and 15); seta FR3 short, hair-like(Fig. 4); seta PA6 short, hair-like (Fig. 4); MN with additional setae(Fig. 8); cardo with some very short additional setae (Fig. 10); poreMXg proximal on MP2 (Fig. 10); pore MXj medial on MP3 (Fig. 9);MP1, MP2 and LP1 with minute pore-like additional structures(Figs. 9–12); pore LAc medial on LP2 (Fig. 11); seta CO12 medial(Fig. 14); additional setae on CO present (Figs. 13 and 14); seta TR2absent (Fig. 13); seta TR5 short (Fig. 14); abdominal segment X withventral spinulae (Fig. 15).

DescriptionColor (Figs. 1–3). Cephalic capsule and mandibles brown, anten-

nae, maxillae and labium testaceous to light brown; thoracicsclerites light brown, rest of thorax and legs testaceous; abdomentestaceous except terminal hooks brown.

Body (Fig. 1). Elongate, parallel sided, head and pronotumstrongly sclerotized, rest of thorax and abdomen soft. Measure-ments and ratios that characterize the body shape are shown inTable 1.

Head (Fig. 2). Cephalic capsule (Figs. 4 and 5). Subrectangu-lar, longer than broad, parallel-sided with distinct narrow neck;occipital foramen slightly emarginate both dorsally and ventrally;occipital suture present; coronal suture short; frontal suturesU-shaped, extending to antennal bases; posterior tentorial pits vis-ible ventromedially; area near occipital suture with reticulation;FR elongate, anterior margin with three weakly delimited lobes;medial lobe slightly produced anteriorly, with four very inconspic-uous teeth; lateral lobes weakly developed, truncate, not projectedbeyond medial lobe; PA with egg bursters formed by a single cutic-ular spine on each posterolateral surface, and six stemmata at eachside, four dorsal and two ventral (not shown in Figs. 4 and 5 becausethey could not be recognized after the clearing process). Antenna(Figs. 6 and 7). Moderately long, slender, shorter than HW, com-

posed of four antennomeres; A1 shortest, A2, A3 and A4 longest,subequal in length; A3 with two minute structures (probably spin-ulae) on ventrodistal surface, and two subapical flat plates on innermargin, distal one interpreted as the sensorium (A3′) which does

M.C. Michat et al. / Revista Brasileira de Entomologia 60 (2016) 231–237 233

Figures 1–3. Enhydrus sulcatus, first-instar larva. (1) Habitus, dorsal view, (2) head, dorsaFigs. 2 and 3.

Table 1Measurements and ratios for the first-instar larva of Enhydrus sulcatus.

Measure Instar I (n = 3) Measure Instar I (n = 3)

TL (mm) 8.00–9.40 A/MP 1.03–1.06MW (mm) 0.65–0.80 GA/MP1 0.44–0.50HL (mm) 1.07–1.16 PPF/MP1 0.60–0.66HW (mm) 0.76–0.85 MP1/MP2 0.83–0.91FRL (mm) 0.79–0.87 MP3/MP2 1.15–1.17OCW (mm) 0.50–0.58 MP/LP 1.16–1.19COL (mm) 0.28–0.30 LP2/LP1 0.86–0.92HL/HW 1.36–1.40 L3 (mm) 2.41–2.52HW/OCW 1.46–1.54 L3/L1 1.23–1.25COL/HL 0.26 L3/L2 1.09–1.10FRL/HL 0.74 L3/HW 2.96–3.16A/HW 0.85–0.95 L3 (CO/FE) 1.35–1.40A1/A3 0.21–0.28 L3 (TI/FE) 0.68–0.71A2/A3 0.98–1.02 L3 (TA/FE) 0.81–0.84A4/A3 0.89–0.96 L3 (CL/TA) 0.51–0.56

nmlbm

MNL/MNW 2.83–3.35 MH/LH 1.00–1.04MNL/HL 0.49–0.53

ot protrude; A4 with a subapical flat sensorial plate on inner

argin, accompanied by two minute structures (probably spinu-

ae or pores). Mandible (Fig. 8). Relatively elongate, curved, broadasally, distal half projected inward, apex sharp; inner marginore or less toothed on distal third; retinaculum absent, although

l view, (3) abdomen, ventral view. Scale bars = 2.00 mm for Fig. 1 and 0.50 mm for

one of the teeth may be interpreted as that structure; mandibularchannel present. Maxilla (Figs. 9 and 10). Well developed, promi-nent; cardo strongly developed, subquadrate, bearing a group ofminute spinulae on dorsal surface; stipes short, broad, subtrape-zoidal, bearing a lacinia and GA on distal inner margin and a PPFon distal outer margin; lacinia well developed, slender, indentedapically; GA elongate, two-segmented, basal segment shorter, glo-bose, distal segment longer, narrow, apically pointed; PPF short,palpomere-like, projected apicodorsally in a subtriangular pro-cess; MP long, composed of three palpomeres separated by obliquejoints; MP1 and MP2 shortest, subequal in length, MP3 longest.Labium (Figs. 11 and 12). Well developed, prominent; prementumdivided longitudinally into two subcylindrical halves fused basally,each half bearing minute spinulae on dorsal surface and projectedapicodorsally in a subtriangular process; LP long, composed of twopalpomeres separated by oblique joints; LP1 slightly longer thanLP2.

Thorax (Fig. 1). Long, narrow, subcylindrical; pronotum longestand broadest, meso- and metanotum subequal; protergite welldeveloped, covering almost whole segment dorsally, anterior

and posterior margins truncate, lateral margins rounded; mem-brane between pronotum and mesonotum with a single narrowtransverse sclerite; both sclerites with sagittal line, lacking ante-rior transverse carina; meso- and metaterga lacking sclerites;

234 M.C. Michat et al. / Revista Brasileira de

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Figures 4–5. Enhydrus sulcatus, first-instar larva. (4) Cephalic capsule, dorsal view,(5) cephalic capsule, ventral view. Numbers and lowercase letters indicate pri-mary setae and pores, respectively. Conspicuous additional setae indicated by solidsc

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on ventrointernal margin; LP2 with one pore (LAc) on dorsomedial

quares. Inconspicuous additional setae not labeled). EB, egg bursters; FR, fronto-lypeus; PA, parietal; TP, tentorial pits. Scale bar = 0.30 mm.

entral surface membranous except for a single large subrect-ngular sclerite covering anterior half of prothorax, and smallclerites on the regions of articulation of coxae; spiracles absent.egs (Figs. 13 and 14). Long, slender, composed of six segments; L3ongest, L1 shortest; CO elongate, robust, TR short, lacking annu-us, FE, TI and TA slender, subcylindrical, PT with two long, slender,lightly curved claws, posterior claw shorter than anterior claw;pinulae absent.

Abdomen (Fig. 1). Ten-segmented, long, narrow, subcylindrical,

ntirely membranous; segments I–VIII similar in shape and sizesegment VIII somewhat smaller), bearing a tracheal gill on pos-erolateral angle; segment IX visibly narrower, bearing two tracheal

Entomologia 60 (2016) 231–237

gills on posterolateral angle; tracheal gills slender, almost devoid ofspinulae (exception: 2–3 at tip), those of segment IX longer than theothers; segment X (Figs. 3, 15) smallest and narrowest, pygopod-like, arising on posteroventral surface of segment IX, not carryinggills, bearing ventral spinulae and four strongly sclerotized terminalhooks which are subequal in length (Figs. 3, 15–17).

Chaetotaxy. Frontoclypeus (Fig. 4). Medial lobe of anterior mar-gin with two spine-like setae (FR10, FR11), one short hair-like seta(FR5), and one pore (FRd); lateral lobe of anterior margin with twominute spine-like setae (FR6, FR9), two short hair-like setae (FR7,FR8), and one pore (FRe); lateral margin with two short hair-likesetae (FR1, FR2) and two pores (FRa, FRc) on distal third and oneshort hair-like seta (FR3) on basal third; central portion with oneshort hair-like seta (FR4); surface with numerous short hair-likeadditional setae. Parietal (Figs. 4 and 5). Dorsal surface with oneshort hair-like seta (PA10) posterior to antennal base, a longitu-dinal row of four short hair-like setae (PA5, PA7, PA8, PA9) closeto frontoclypeal margin, two short hair-like setae (PA4, PA6) onbasal third, close to egg bursters, and three short spine-like setae(PA1, PA2, PA3) and two pores (PAa, PAb) on neck region; ventralsurface with three short hair-like setae (PA17, PA18, PA19) and onepore (PAo) on anteromedial region, four short hair-like setae (PA11,PA12, PA13, PA14) and four pores (PAf, PAg, PAh, PAi) on anterolat-eral angle, one short hair-like seta (PA16) and one pore (PAk) at midlength, and one long hair-like seta (PA15) and one pore (PAm) onbasal third; dorsal and ventral surface with numerous short hair-like additional setae (except on neck region). Antenna (Figs. 6 and 7).A1 with three pores (ANa, ANb, ANc) on dorsal surface and twopores (ANd, ANe) on ventral surface; A2 with one minute pore (ANi)on ventromedial region; A3 with one pore (ANf) on dorsomedialregion, one short hair-like seta (AN2) on dorsodistal portion andone short hair-like seta (AN3) on ventrodistal portion; A4 with onepore (ANg) on dorsodistal portion and two minute spine-like setae(AN4, AN5) at apex. Mandible (Fig. 8). Dorsal surface with one pore(MNa) on basal fourth, two pores (MNb, MNc) at mid length, oneshort hair-like seta (MN1) on distal third, and two short hair-likesetae (MN2 and one additional seta) near tip; dorsal surface withnumerous minute additional setae. Maxilla (Figs. 9 and 10). Cardowith one short hair-like seta (MX1) and some very short additionalsetae on ventral surface; stipes with one short hair-like seta (MX3)on dorsoexternal margin, one short hair-like seta (MX2) and twopores (MXa, MXb) on ventroexternal margin, one very short seta(MX4) ventrally near base of lacinia, and two short curved spine-like setae (MX5, MX6) dorsally at base of lacinia; proximal segmentof GA with one short hair-like seta (MX7) on anteroventral mar-gin and one short hair-like additional seta on dorsal margin; distalsegment of GA with one short hair-like seta (MX8) on dorsoproxi-mal surface, two pores (MXd, MXh) on ventroproximal surface, andone short hair-like seta (MX9) and one minute additional seta nearapex; PPF with one short hair-like seta (MX10) on ventral margin;MP1 with one pore (MXe) and one minute seta (MX13) on ventro-proximal portion, and one pore (MXf) on dorsodistal portion; MP2with one pore (MXg) on ventroproximal portion and two short hair-like setae (MX11, MX12) on dorsodistal and ventrodistal portionsrespectively; MP3 with one pore (MXj) on dorsoexternal marginand one short hair-like seta (MX14) near apex; palpomeres withseveral minute pore-like additional structures both on dorsal andventral surface. Labium (Figs. 11 and 12). Prementum with threeshort hair-like setae (LA3, LA4, LA5) and one pore (LAa) on dorsodis-tal surface, one short hair-like seta (LA2) on ventrodistal surface,and one minute seta (LA1) on ventroproximal surface; LP1 with oneminute seta (LA9) on ventroproximal portion and one pore (LAb)

portion and one short hair-like seta (LA12) near apex; palpomereswith several minute pore-like additional structures both on dorsaland ventral surface. Thorax. Surface of thoracic terga with several

M.C. Michat et al. / Revista Brasileira de Entomologia 60 (2016) 231–237 235

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igures 6–12. Enhydrus sulcatus, first-instar larva. (6) Right antenna, dorsal view, (710) left maxilla, ventral view, (11) labium, dorsal view, (12) labium, ventral view. Netae indicated by solid squares (except for minute additional setae on the mandibl

air-like setae. Legs (Figs. 13 and 14). Anterior surface of CO withix very short spine-like setae (CO1, CO2, CO3, CO4, CO5, CO17) andne very short hair-like seta (CO18) on proximal portion, one longair-like seta (CO6), one short hair-like seta (CO7) and one poreCOa) on medial portion, and three short hair-like setae (CO8, CO9,O10) on distal portion; posterior surface of CO with four very shortpine-like setae (CO13, CO14, CO15, CO16) on proximal portion, onehort hair-like seta (CO12) on medial portion, and one short spine-ike seta (CO11) and one pore (COd) on distal portion; dorsal surfacef CO with several short hair-like additional setae that obscure the

ecognition of setae CO7 and CO18, which are therefore tentativelyssigned; anterior surface of TR with one short hair-like seta (TR1)n dorsal margin, one long (TR4) and one short (TR3) hair-like setaen ventrodistal margin, five pores (TRa, TRb, TRc, TRd, TRe) on

ntenna, ventral view, (8) right mandible, dorsal view, (9) right maxilla, dorsal view,rs and lowercase letters indicate primary setae and pores, respectively. Additional

ch are not labeled). SP, spinulae. Scale bars = 0.15 mm.

central portion, and one additional pore on ventral margin; pos-terior surface of TR with one short hair-like seta (TR7) on ventralmargin, and two short hair-like setae (TR5, TR6) and two pores (TRf,TRg) on distal margin; anterior surface of FE with one short spine-like seta (FE1) and one pore (FEb) on proximal portion, and twoshort spine-like setae (FE2, FE3) on distal portion; posterior surfaceof FE with two short spine-like setae (FE4, FE5) and one short hair-like seta (FE6) on distal portion; anterior surface of TI with one shorthair-like seta (TI1) on proximal portion and three short spine-likesetae (TI2, TI3, TI4) on distal portion; posterior surface of TI with

one pore (TIa) on central portion, and two short spine-like setae(TI5, TI6) and one long hair-like seta (TI7) on distal portion; ante-rior surface of TA with three short spine-like setae (TA2, TA3, TA4),one minute seta (TA7), and three pores (TAa, TAc, TAd) on distal

236 M.C. Michat et al. / Revista Brasileira de Entomologia 60 (2016) 231–237

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igures 13–17. Enhydrus sulcatus, first-instar larva. (13) Left metathoracic leg, anteiew, (16) medial hook, lateral view, (17) lateral hook, lateral view. Numbers and londicated by solid squares. Additional pore on trochanter indicated by solid triangle

ortion; posterior surface of TA with three short spine-like setaeTA1, TA5, TA6) and three pores (TAb, TAe, TAf) on distal portion;nterior surface of PT with one long spine-like seta (PT1) onasoventral portion; posterior surface of PT with one short spine-

ike seta (PT2) on basoventral portion. Abdomen. Segments I–IXith some short hair-like setae on dorsal and ventral surfaces;

racheal gills with one short spine-like seta near base, few shortair-like setae along their length, and one long hair-like seta atip; segment X (Fig. 15) with two short spine-like setae, two longpine-like setae, and four pores on ventral surface; terminal hooksFigs. 16 and 17) with two pores at distal third of ventral margin.

iscussion

The so far unknown larva of the genus Enhydrus is documentedn this contribution which represents an additional step in the study

f the larval morphology of the Gyrinidae. However, as the larvaef several gyrinid genera are still unknown or remain insufficientlyocumented, in particular some key genera such as Spanglerogyrusolkerts, 1979 and Heterogyrus Legros, 1953, the phylogenetic value

iew, (14) right metathoracic leg, posterior view, (15) abdominal segment X, ventralase letters indicate primary setae and pores, respectively. Additional setae on coxailla on abdominal segment X not labeled. Scale bars = 0.15 mm.

of some of the characters mentioned below should be taken withcaution.

The larvae of Enhydrus bear egg bursters on the parietal,one additional sensorial plate on the third antennomere, a well-developed cardo and lacinia, a completely divided prementum,lateral abdominal tracheal gills, and four terminal hooks on thepygopod. These characters were considered as potential autapo-morphies of the Gyrinidae by previous authors (Beutel andRoughley, 1994, 2005; Archangelsky and Michat, 2007; Michat andGustafson, 2016). In particular, the presence of well developed,spiniform egg bursters on the posterolateral surface of the pari-etal in Enhydrus larvae reinforces the hypothesis that this structureis extended within the family.

The Dineutini are probably the tribe with better knownlarval morphology, due to detailed descriptions (including pri-mary chaetotaxy) of the genera Andogyrus (Arndt et al., 1993;

Archangelsky and Michat, 2007) and Macrogyrus (Michat andGustafson, 2016). The larvae of Dineutus were also partially exam-ined for chaetotaxy, although the chaetotaxy pattern of this genuswas not formally described (Archangelsky and Michat, 2007).

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M.C. Michat et al. / Revista Brasile

onsidering the description of Enhydrus provided herein, only thearvae of the genus Porrorhynchus remain unknown. The first instarf Enhydrus shares with those of the other known Dineutini generahe presence of numerous very short to minute additional setaen the dorsal and external surfaces of the mandible (Fig. 8), theresence of additional setae on the cardo (Fig. 10), the presencef numerous minute pore-like additional structures on the ulti-ate maxillary and labial palpomeres (Figs. 9–12), the submedial

osition of the primary seta CO12 on the coxa (Fig. 14), and thebsence of the primary seta TR2 on the trochanter (Fig. 13). Beutelnd Roughley (1994) mentioned an extremely long and slenderardo as a possible autapomorphy of Dineutini. According to Michatnd Gustafson (2016), however, this character is not so clear in therst instar, although it is more evident in the third instar. As onlyrst instars of Enhydrus were available for study, the state of thisharacter remains to be tested when later instars are discovered.

Larvae of Enhydrus can be distinguished from those of thether known genera of Dineutini by the following combinationf characters: neck constriction present (=Andogyrus and Dineu-us, absent in Macrogyrus) (Figs. 2, 4 and 5); posterior margin ofacinia not dentate (=Dineutus, dentate in Andogyrus and Macro-yrus) (Figs. 9 and 10); first and second maxillary palpomeres andrst labial palpomere bearing minute pore-like additional struc-ures (absent in Andogyrus, Dineutus and Macrogyrus) (Figs. 9–12);abial pore LAc submedial (=Andogyrus and Dineutus, distal in Macr-gyrus) (Fig. 11); additional setae on coxa present (=Andogyrus,bsent in Dineutus and Macrogyrus) (Figs. 13 and 14); tracheal gillsot plumose (plumose in Andogyrus, Dineutus and Macrogyrus);bdominal segment X with ventral spinulae (absent in Andogyrus,ineutus and Macrogyrus) (Fig. 15). Although the presence of addi-

ional setae on the cardo is common to all known dineutine genera,nhydrus has several of these setae whereas the other three generaave only one seta (accidentally overlooked in Archangelsky andichat, 2007). On the other hand, although the larvae of all known

ineutine genera bear pore-like additional structures on their palpi,n Enhydrus these structures are present in all maxillary and labialalpomeres, whereas in the other three genera they are restrictedo the ultimate palpomeres (Michat and Gustafson, 2016).

onflicts of interest

The authors declare no conflicts of interest.

Entomologia 60 (2016) 231–237 237

Acknowledgements

The work of Mariano C. Michat was supported by CONICET underGrant PIP-2011-1087, by ANPCyT under Grant PICT-2014-0853,and by Universidad de Buenos Aires under Grant UBACyT-20020150100170BA. Financial support was also provided by theNatural Sciences and Engineering Research Council of Canada inthe form of a discovery research grant to Yves Alarie.

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